Power circuit breakers in the low-voltage range should be suitable for use in as wide a rated-current range as possible, for example 200 A to 6300 A. It should therefore be possible to select their rated current. By setting a specific rated current, the appropriate overcurrent release parameters are set for a selected rated current. The overcurrent release may thus be physically the same for the whole rated-current range.
It is known for overcurrent releases to be equipped with a plug-in rated-current plug connector (rating plug) which is fitted with resistors, for example, and by use of which one or more characteristic values can be determined for the switch. It is thus not possible to operate the switch without the rated-current plug connector.
A rated-current plug connector is known, for example, from U.S. Pat. No. 4,649,455. If the rated-current plug connector according to this solution is taken out of the switch, for example in order to replace it with a rated-current plug connector having different user settings, the tripping unit sets itself automatically to a minimum tripping value until a rated-current plug connector has been inserted again. In the simplest case, this is achieved by a setting resistor, which is connected electrically in parallel with the setting resistors in the rated-current plug connector, being arranged fixedly in the tripping unit and determining the rated current when the rated-current plug connector is removed.
In order to prevent unsuitable rated-current plug connectors, which would set a rated current outside the rating limits for the power circuit breaker, from being used, it is known, for example from U.S. Pat. No. 5,027,091, to mechanically code the rated-current plug connector using key-coding.
DE-A 198 45 825 also discloses a solution which uses electrical coding so that unsuitable characteristic values for the rated-current plug connector are not transferred to the tripping unit but, when an attempt is made to use such a rated-current plug connector, a signal is output. The signaling device should be arranged on the rated-current plug connector. A fault signal is output only when the rated-current plug connector is inserted. It is not possible in this way to indicate faults such as the absence of a contact connection between the rated-current plug connector and the tripping unit or the complete absence of a rated-current plug connector.